1. Field of the Invention
The present invention relates to a method of generating a gradation correction curve which is employed for correcting the gradation character of a given image.
2. Description of Prior Arts
As well known in the art, an image having gradation is read with a photoelectric image reader in order to reproduce the image on a photosensitive film or another medium. The image data which is obtained through image reading is often subjected to a gradation correction so that the gradation character of the image is corrected into desirable one. The gradation correction is carried out through a gradation correction curve which is determined in the basis of density distribution on the image and other characters. The determination of the gradation correction curve has been attained by a skillful operator since the determination is a sensitive work. Therefore, expected is development of an apparatus operable to automatically generate a gradation correction curve.
In order to develop such an automatic apparatus, it is required to establish a method of generating gradation correction curves which is suitable for automatic generation of the gradation correction curves. In particular, the following three problems should be solved:
(1) How highlight and shadow points are determined in the automatic generation of the gradation correction curves?
(2) How the density range of an original image is reflected into the gradation correction?
(3) How the sensitive character around highlight and shadow points are provided in gradation correction curves?
U.S. Pat. No. 4,792,979 which has been assigned to the applicant of the present invention answers the above-indicated problems to some extent. However, more effective are required to fully solve the problems.